void main(){
  /**
   * 运算符： +，- , * , / , ~/ (除法取整), %
   * 常用属性：isNaN,isEven,isOdd
   * 常用方法：abs(),round(),floor(),ceil(),toInt(),toDouble()
   */
  num count = 3; //num是数字型的基类
  count=3.15;
  print(count);

  int age=30; //整型
  print(age);

  double score=33.1;  //浮点型
  score=100;
  print(score);

  int a=10,b=20;
  double c=3.14;
  print(a+b);
  print(a-b);
  print(a*b);
  print(a/b);
  print(a~/b);
  print(a%b);
  print(a.isOdd);
  print(c.toInt());
}